Decorative substrates such as decorative laminates are widely used in both residential and commercial applications particularly where both an aesthetically pleasing appearance and functionality are desired. Examples of applications for decorative laminates include, but are not limited to, walls, countertops, furniture, paneling, and flooring.
Decorative laminates are classified into two categories: high pressure decorative laminates (HPDL) and low pressure decorative laminates (LPDL). As is known in the industry, high pressure decorative laminates are typically manufactured or laminated under heat and a specific pressure of more than 750 psig. Low pressure decorative laminates are typically manufactured at a specific pressure of about 300 psig. Also, high pressure decorative laminates are generally relatively thin, typically comprising a decorative surface and a phenolic resin impregnated kraft paper core. Low pressure density laminates are normally thermally bonded to a rigid substrate such as particle board or medium density fiberboard (MDF). High pressure decorative laminates are bonded to a rigid substrate by an adhesive and require an additional fabrication step. Low pressure decorative laminates are comprised of a decorative surface bonded to a substrate such as particleboard or MDF. A low pressure decorative laminate does not have a supporting core layer as does a high pressure decorative laminate. Also, there is typically only a single laminating or pressing operation during fabrication of a low pressure decorative laminate.
High pressure and low pressure decorative laminates are traditionally manufactured in heated, flat-bed hydraulic presses. As is known in the industry, high pressure laminates are typically pressed as multiple sheets in press “packs” or “books” in a multi-opening press which is usually steam or high pressure hot water heated, and water cooled, with a 30 to 60 minute thermal cycle and 130° C. (266° F.) to 150° C. (302° F.) top temperature. Low pressure decorative laminates are typically pressed as a single sheet or “board” in a single opening press using an isothermal, hot discharge “short cycle” of 30 to 60 seconds with press heating platen temperatures of 180° C. (356° F.) to 220° C. (428° F.). Continuous laminating or “double belt” or “double band” presses for decorative laminate manufacture have similar “cycle” times and temperatures as those employed for low pressure decorative laminates. Continuous laminates are relatively thin, without direct bonding to a substrate. Continuous laminates require a second fabrication step as do conventional high pressure decorative laminates.
The typical construction of a continuous laminate is a melamine-impregnated, alpha cellulose overlay plus a paper superimposed over one or more phenolic resin impregnated papers. The thickness of the laminate, which is normally in the 1/32″ range, is ultimately determined by the layers of papers and the resulting amount of resin absorbed. When the sheet is pressed, a steel caul plate is used to create a surface finish ranging from high gloss smooth to fully textured. Continuous laminates can be rolled, but only into larger diameter rolls. When decorative papers are prepared for use in lamination they are typically digitally printed, offset printed, gravure printed, pad coat printed or silk screened.
There are known methods for transferring a design formed on a transfer sheet to a substrate using sublimation dyes. Sublimation is a process through which solids transform directly into gases without going through an intermediate liquid state. For example, a sheet of cellulose web material such as paper impregnated with a thermosetting resin is applied to at least one surface of a substrate. While the surfaces are in contact, the resin-impregnated paper is consolidated to the substrate under heat and pressure such that the resin seeps into the pores of the substrate to form a thermofused substrate. Thus, the term “thermofuse” generally refers to applying heat and pressure to bond material together. A transfer sheet is brought into contact with the surface of the thermofused substrate. Heat and pressure are applied to the transfer sheet and thermofused substrate through a sublimation process. The transfer sheet is separated from the surface of the thermofused substrate. Optionally, a protective coating is applied over the surface of the substrate showing the transferred design. The design is transferred and penetrated into the surface of the substrate at a temperature and a pressure readily determined by one of ordinary skill in the art.
U.S. Pat. No. 6,300,279 describes a method for transferring a decorative sublimation dye design formed on a transfer sheet to a wood substrate by applying a sheet of cellulose web material impregnated with a thermosetting resin to at least one surface of a wood substrate.
U.S. Pat. No. 6,596,116 describes a method for transferring a sublimation design formed on a transfer sheet to a continuous laminate by using a sublimation dye.
There are also practical advantages to coloring a substrate with a sublimation dye as opposed to simply adding a coat of color film to the surface of a substrate. The dye sublimation method results in more permanent color, as there is no film coat to abrade or fade. By using a sublimation dye that vaporizes when heated, the decorative design may be made to penetrate or bleed into the body of the substrate. Also, the dye sublimation method does not physically alter the surface of the substrate, for instance, adding a coat of color film would. Still yet, there is no significant change in the weight of the substrate colored.
Although polyester tends to have performance properties very similar to melamine, it is known that in contrast to melamine, polyester is receptive to image imprinting with sublimation dyes. Polyester based laminates and decorative surfaces readily receive imaging from dye sublimation printing. Within the crystal matrix of the polyester structure are available sites for the sublimed particles to reside after cooling. In the industry, the dye sublimation printing process has not worked effectively with melamine based laminates. Since the high pressure laminate market widely accepts melamine based laminates as the dominate market standard, the ability to use dye sublimation printing on a melamine based laminate would have significant commercial benefits. A primary benefit would be to use the dye sublimation imaged product as a standard laminate in an application. A polyester resin material is difficult, if not impossible, to thermofuse to certain substrates that are requisite to furniture manufacturing, architectural products, and other industries. A melamine resin can more readily achieve a thermofused bond due to more compatible condition requirements such as temperature and pressure to create a chemical bond, as necessary to thermofuse substrates such as particle board, engineered woods, phenolic backers, cement board, plastics, polymers, and various other substrates.
Furthermore, melamine has greater market acceptance in fields where a thermofused or laminated substrate is utilized than does polyester. While polyester resin is capable of thermofusing, alone it does not contain adequate properties such as durability, and polyester treated material is typically more expensive than melamine treated material. Another difficulty with thermofusing polyester lies in thermofusing the same onto a phenolic back in that the required cure temperature and pressure required for polymerization of phenolic and polyester are different. Thus, there is a need to be able to make a thermofused bond onto various substrates, including phenolic, which is so difficult to achieve with polyester.
However, until now, melamine could not effectively be used for imaging with sublimation dyes. The present invention attempts to solve this problem by achieving a modified melamine resin for use in sublimation dye imaging that mimics the ability of polyester to accept a dye.